L2TP Users cannot Open Web Pages Because of MTU of MA5200G

Latest reply: Mar 8, 2016 18:28:04 1202 1 0 0

Topology: PC--MA5200G(LAC)--Website Server
After successful dial-up, users could ping through to the web site address connecting to LNS, but they cannot open the web pages, even though entering IP address in IE. 

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Osaideo Created Mar 8, 2016 18:28:04 Helpful(0) Helpful(0)

Handling Process
Solution: 
1. Load a software at PC to limit the value of MSS; 
2. Limite the MTU at the interface of LNS connecting to website server. 
Root Cause
1. The interface of router has a MTU, and the packet with a value larger than MTU will be fragmented, which may cause a lot of problems, so it is advisable to avoid fragments in transmission of packets;
2. The MSS value (MSS=MTU-IP-TCP) negotiated by PC and website server is too large, and LNS needs to fragment the IP packets.  However, LNS only adds L2TP header to the first packet fragmented, and the later will be omitted. So, MA5200G will not recognize the packets without L2TP header, which will be discarded then.  The result makes PC fail to receive the relevant packets sent by LNS, and so the web page cannot be opened. 

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